Safety circuit for electronic machine controls of the plug-in modular type

ABSTRACT

A safety circuit for preventing an electronic control from supplying signals to operate a machine whenever a circuit card is removed from the control. Removal of a circuit card causes a flip-flop to be set and to remain in that state until the removed card is re-inserted, and a manually operated push button is actuated to reset the flip-flop. Operation of the push button sounds a warning bell and resets the flip-flop after a predetermined time.

United States Patent Vinch et al.

SAFETY CIRCUIT FOR ELECTRONIC MACHINE CONTROLS OF THE PLUG- IN MODULAR TYPE lnventors:

Assignee:

Filed:

Appl.

Angelo N. Vinch, Warren; David A.

Kamulski, Detroit, both of Mich.

Westinghouse Electric Corporation,

Pittsburgh, Pa.

Feb. 11, 1971 References Cited u.s. Cl. ..301/149, 317/135, 340/421 Int. Cl. ..H02j

Field 01 Search ..3l7/135; 307/149; 340/421 UNITED STATES PATENTS l-Iefti ..317/l35 R [451 Sept. 12, 1972 Primary Examiner-L. T. Hix Attorney-A. T. Stratton and Clement L. Hale [5 7] ABSTRACT A safety circuit for preventing an electronic control from supplying signals to operate a machine whenever a circuit card is removed from the control, Removal of a circuit card causes a flip-flop to be set and to remain in that state until the removed card is re-inserted, and a manually operated push button is actuated to reset the flip-flop. Operation of the push button sounds a warning bell and resets the flip-flop after a predetermined time.

13 Claims, 1 Drawing Figure SAFETY CIRCUIT FOR ELECTRONIC MACHINE CONTROLS OF THE PLUG-IN MODULAR TYPE This invention relates to machine control circuits and particularly to a safety circuit for an electronic control of the modular plug-in type.

One type of electronic control for a machine, such as a transfer mechanism, comprises a plurality of plug-in type circuit modules, or cards, which are mounted within a control panel. Each module or card contains various electronic components connected in circuit on the card. These circuits terminate in a plurality of connectors on the card which are mechanically engageable with corresponding terminals in the control panel to establish electrical connections therebetween. The terminals in the panel are wired in accordance with the control design to establish circuit connections between the various plug-in cards and the machine for controlling the operation of various machine elements in predetermined sequence. The particular advantage of plug-in type cards resides in the ease with which a faulty circuit component may bereplaced; that is, a defective electronic circuit may be corrected by bodily removing the card which contains the defective circuit and replacing it by a new, identical card.

A particularly serious problem can occur if a circuit card is removed and replaced while the control is operational. The dimensions of the problem are increased in the case of a very large transfer machine which has a large number of stations along its length and an electronic control for each station which may be remotely located relative to its respective station. With a circuit card removed from one of the electronic controls, the station with which that control is associated is rendered inoperative. If power is maintained to the electronic control, re-insertion of the card can now render the station operational. Hence, personnel working at what appears to them to be an inoperative station, with the card removed, are exposed to unexpected operation of that station when the card is re-inserted.

Therefore, the primary object of this invention is to provide a circuit for electronic controls of the aforementioned type which provides-increased safety to personnel.

Another object of the invention is to provide a safety circuit for controls of the aforementioned type which upon removal and re-insertion of a circuit card 'prevents further operation of the machine until the control has been reset and a warning signal sounded.

Other objects and features of the invention will become apparent in the following description and drawing which shows a diagram partly pictorial and partly schematic of the safety circuit of the present invention.

Referring now to the drawing, an electronic control for a machine such as a transfer mechanism includes a pair of circuit cards, or modules, and 12 shown in position for insertion into a pair of panel-mounted terminal blocks 14 and 16 respectively. A plurality of terminals 18 are aligned in a vertical row along the rear edge of each card 10 and 12. When each card is inserted into its respective terminal block, each terminal 18 registers with a corresponding terminal 20 in each block 14 and 16 to establish an electrical connection therebetween.

The terminals 18 on card 10 are electrically connected by conductors 24 to a plurality of circuit elements thereon which include: a control logic circuit 22, to which terminals and 18b are electrically connected by conductors 24a and 248, an and-gate 26 whose two input terminals are electrically connected to the output of control logic 22 and to terminal 18h by means of conductors 24d and 24!: respectively, and a DC-AC converter 28 whose input is connected to the output of gate 26 by conductor 24c and whose output is connected to terminal 18f by conductor 24f. Typically, control logic 22 comprises a plurality of electronic logic elements, such as and-gates, or-gates or inverters, arranged to provide a DC control signal at line 24d in accordance with the DC input signals supplied to it, as by conductors 24a and 24b. And-gate 26 in turn transmits this control signal to conductor 24c so long as a signal is present at conductor 24h. Converter 28 may comprise, for example, a triac which connects an AC line (not shown) to terminal 18f through conductor 24f in response to the presence of a DC signal at line 24e. Terminals 18c and 18d are shorted together by conductor 24g and are engageable with terminals 200 and 20d. Terminals 18g and 18j are adapted to register with terminals 20g and 20j on card 10 to supply DC power to the circuitry thereon, as will soon be more clearly apparent.

Card 12 also includes terminals 180 and 18d which are similarly shorted together by conductor 24g, and terminals 183 and 18j for supplying DC power.

Terminals 20a and 20b in block 14 are adapted to engage with terminals 180 and 18b respectively on card 10 and are electrically connected by wires 30a and 30b to switches (not shown) on the machine. Terminal 20f in block 14 is adapted to register with terminal 18f on card 10 and is electrically connected by wire 30f to a solenoid-actuated valve 31 on the machine. When valve 31 is operated by supplying current through wire 30f, pressure fluid is admitted to a hydraulic cylinder to advance a machine slide. Terminal 200 in terminal block 14, which is engageable with terminal 18c on card 10, is electrically connected to the positive terminal of a 24 VDC power supply 32 by wire 30c. Terminal 20d in terminal block 14, which is engageable with terminal 18d on card 10, is in turn wired to terminal 20c in terminal block 16. Terminals 20c and 20d in block 16 are engageable with terminals 180 and 18d respectively on card 12. Wire 30e electrically connects terminal 20d in terminal block 16 with terminals 20 in blocks 14 and 16 and therefore when both cards are inserted into their respective blocks, power supply 32 is electrically connected to terminals 183 and l8j on each card.

Wire 30:: also connects with one terminal 33 of a pair of input terminals 33 and 35 of a flip-flop 34. The other, or reset, terminal 35 of flip-flop 34 is supplied by a reset circuit 36. Circuit 36 comprises a push-button switch 38 which, when operated, connects supply 32 with a warning bell 40 and a timer 42. After switch 38 has been depressed for a preselected time, timer 42 actuates a one shot 44 which triggers terminal 35 to reset flip-flop 34. The output lead 46 of flip-flop 34 is connected to terminal 20h in block 14 which in turn is adapted to register with terminal 18h on card 10.

Describing now the operation of the disclosed embodiment, with cards and 12 inserted into terminal blocks 14 and 16 respectively, power supply 32 supplies voltage to wire 30c through the path comprising the short-circuited terminals 18c and 18d on each card. Wire 30a in turn supplies terminals 18g on each card and also terminal 33 of flip-flop 34. Assuming that flipflop 34 is in the set state, lead 46 supplies no signal to and-gate 26. As a result, and-gate 26 is prevented from actuating converter 28 which is the sole means by which valve 31 is operable. This is true regardless of the signal supplied to and-gate 26 by control logic 22. Hence, in this condition, it is impossible for the control to operate the machine slide which is controlled by valve 31.

Valve 31 may be rendered operable by operating push-button 38. Operation of push button 38 starts timer 42 and rings warning bell 40 to alert personnel in the vicinity of the machine that operation of the machine is about to be initiated. When timer 42 times out, it operates one shot 44 to reset flip-flop 34. In the reset state, flip-flop 34 supplies a signal at line 46 to and-gate 26. As a result, and-gate 26 may be operated in accordance with signals received from control logic 22 along conductor 24d. Hence, control logic 22 now operates valve 31 in response to the actuation of the previously mentioned switches (not shown) on the machine which are electrically connected to control logic 22 by wires 30a and 30b.

Removal of either circuit card from its terminal block disconnects supply 32 from wire 30E. Flip-flop 34 is constructed to switch to the set state in response to loss of this voltage and to remain in the set state until the removed circuit card is re-inserted and a reset signal is applied at input terminal 35. Thus at first, when the removed card is re-inserted, the circuit path between supply 32 and wire 30c is re-established and power is supplied to the circuitry on each card through terminals 18g. However, card 10 cannot operate valve 31 because there is no signal present at lead 46 which enables and-gate 26 to respond to the control signal from control logic 22. Now when push button 38 is operated a warning is sounded by bell 40 and flip-flop 34 is reset after timer 42 times out. With flip-flop 34 reset, a signal is applied along lead 46 to and-gate 26 to permit the operation of valve 31 in response to the control signal supplied by control logic 22. In this way, operation of the machine slide is prevented until an operator manually actuates push button 38 to provide a warning signal.

While the invention has been described for only one particular element of a machine, it should be appreciated that any number of terminal blocks and their corresponding circuit cards may be connected together in the same fashion to disable various portions of the control which operate various machine elements. Also, it should be recognized that the safety circuit, while being admirably suited for use with a large machine having portions which are not visible from the location of push button 38, may be used on any type of electronic control in which plug-in type cards control a moving element of a machine. The safety circuit may itself be mounted on a plug-in card, if desired.

We claim:

1. In combination an electronic control of the type comprising a plurality of plug-in type circuit cards mechanically engageable with a plurality of terminals in a card-mounting structure, a machine having an operable machine element, transducer means responsive to the operation of said machine, means electrically connecting said electronic control with said machine, one of said circuit cards being a control circuit card having input terminals electrically connected to said transducer means for supplying an operating signal to operate said machine element in response to signals supplied by said transducer means, means on at least one of said cards and said mounting structure forming a complete circuit path when said last-mentioned card is engaged with terminals in the structure, safety circuit means switchable between set and reset states, said safety circuit means being switched to the set state in response to the interruption of said circuit path by removal of said one card forming said path from the mounting structure, means electrically connecting said safety circuit means with said control circuit means for preventing said control circuit means from supplying said operating signal when said safety circuit means is in the set state, and reset circuit means electrically connected to said safety circuit means for switching said safety circuit means from the set state to the reset state, said safety circuit means being resettable only when said circuit path is complete.

2. The combination of claim 1 wherein said control circuit card comprises DC logic means adapted to receive said signals supplied by said transducer means for providing a DC control signal and means responsive to said DC control signal for supplying said operating signal and wherein said means electrically connecting said safety circuit means with said control circuit means for preventing said control circuit means from supplying said operating signal comprises means for preventing said DC control signal from being supplied to said means for supplying said operating signal when said safety circuit means is in the set state.

3. The combination of claim 2 wherein said means for preventing said DC control signal from being supplied to said means for supplying said operating signal comprises an and-gate.

4. The combination of claim 3 wherein said and-gate comprises two input terminals, one of said input terminals being electrically connected to the output terminal of said DC logic means, the other of said input terminals being electrically connected to said safety circuit means.

5. The combination of claim 4 wherein said means responsive to said DC control signal for supplying said operating signal comprises DC-AC converter means for supplying an AC operating signal to operate said machine element.

6. The combination of claim 1 wherein said reset circuit means comprises manually movable switch means electrically connected to said safety circuit means for switching the latter to the reset state.

7. The combination of claim 6 including means for supplying an audible warning signal in response to operation of said switch means.

8. The combination of claim 7 including means for delaying the resetting of said safety circuit means in response to operation of said switch means whereby said warning signal is provided before said safety circuit means is reset.

9. In an electronic control for a machine, said control being of the type comprising a plurality of plug-in type circuit cards mechanically engageable with a plurality of terminals in a card-mounting structure, one of said cards being a control circuit card having DC logic means adapted to receive input signals in response to operation of selected elements of said machine and to provide a DC control signal, control circuit means responsive to said DC control signal for supplying an operating signal adapted to operate a particular element of said machine in response to said input signals, that improvement which comprises means on at least one of said cards and said mounting structure forming a complete circuit path when said one card is engaged with terminals in the structure, safety circuit means switchable between set and reset states, said circuit means being switched to the set state in response to the interruption of said circuit path by removal of said one card forming said path from the mounting structure, a reset circuit means electrically connected to said safety circuit means for switching said safety circuit means from the set state to the reset state, said safety circuit means being resettable only when said circuit path is complete, means electrically connecting said safety circuit means with said control circuit means for preventing said control circuit means from supplying said operating signal by preventing said DC control signal from being supplied to said means for supplying said operating signal when said safety circuit means is in the set state.

10. In an electronic control for a machine, said control being of the type comprising a plurality of plug-in type circuit cards mechanically engageable with a plurality of terminals in a card-mounting structure, one of said cards being a control circuit card having DC logic means adapted to receive input signals in response to operation of selected elements of said machine and to provide a DC control signal, control circuit means responsive to said DC control signal for supplying an operating signal adapted to operate a particular element of said machine in response to said input signals, that improvement which comprises means on at least one of said cards and said mounting structure forming a complete circuit path when said one card is engaged with terminals in the structure, a flip-flop logic element switchable between set and reset states, said flip-flop being switched to the set state in response to the interruption of said circuit path by removal of said one card forming said path from the mounting structure, a reset circuit means electrically connected to said flip-flop logic element for switching said flip-flop logic element from the set state to the reset state, an and-gate electrically connecting said flip-flop logic element from the set state to the reset state, an and-gate electrically connecting said flip-flop logic element with said control circuit means for preventing said control circuit means from supplying said operating signal by preventing said DC control signal from being supplied to said control circuit means when said flip-flop logic element is in the set state, said and-gate comprising two input terminals, one of said input terminals being electrically connected to the output terminal of said DC logic means, the other of said input terminals being electrically connected to said flip-flop output terminal, said flip-flop logic element further comprising a pair of input terminals one of said flip-flop input terminals being electrically connected to said reset circuit means, the other of said flip-flop input terminals being electrically connected to said circuit path, said flip-flop logic element being switchable between set and reset states respectively in response to the respective application of signals at said last-mentioned flip-flop input terminal and said first-mentioned flip-flop terminal respectively, said flip-flop logic element being switchable to the reset state to provide a signal at said flip-flop output terminal only when said circuit path is complete, whereby said and-gate permits said DC control signal to be supplied to said control circuit means for supplying said operating signal.

11. In combination an electronic control of the type comprising a plurality of plug-in type circuit cards mechanically engageable with a plurality of terminals in a card-mounting structure, a machine having an operable machine element, transducer means responsive to the operation of said machine, one of said circuit cards being a control circuit card having input terminals electrically connected to said transducer means for supplying an operating signal to operate said machine element including DC logic means adapted to receive said signals supplied by said transducer means for providing a DC control signal in response to signals supplied by said transducer means, means responsive to said DC control signal for supplying said operating signal, means on at least one of said cards and said mounting structure forming a complete circuit path when said last-mentioned card is engaged with terminals in the structure, a flip-flop logic element being switched to the set state in response to the interruption of said circuit path by removal of said one card forming said path from the mounting structure, reset circuit means electrically connected to said flip-flop logic element for switching said flip-flop logic element from the set state to the reset state, an and-gate electrically connecting said flip-flop with said means responsive to said DC signal for preventing said last-mentioned means from supplying said operating signal when said flip-flop logic element is in the set state, said andgate compris ing two input terminals, one of said input terminals being electrically connected to the output terminal of said DC logic means, the other of said input terminals being electrically connected to said flip-flop output terminal, said flip-flop further comprising a pair of input terminals one of. said flip-flop input terminals being electrically connected to said reset circuit means, the other of said flip-flop input terminals being electrically connected to said circuit path, said flip-flop logic element being switchable between set and reset states respectively in response to the respective application of signals at said last-mentioned flip-flop input terminal and said first-mentioned flip-flop terminal respectively,

' said flip-flop logic element being switchable to the reset state to provide a signal at said flip-flop output terminal only when said circuit path is complete.

12. The control of claim 9 wherein said means for preventing said DC control signal from being supplied 13. The control of claim 12 wherein said and-gate comprises two input terminals,one of said input terminals being electrically connected to the output terminal of said DC logic means, the other of said input terminals being electrically connected to said safety circuit means. 

1. In combination an electronic control of the type comprising a plurality of plug-in type circuit cards mechanically engageable with a plurality of terminals in a card-mounting structure, a machine having an operable machine element, transducer means responsive to the operation of said machine, means electrically connecting said electronic control with said machine, one of said circuit cards being a control circuit card having input terminals electrically connected to said transducer means for supplying an operating signal to operate said machine element in response to signals supplied by said transducer means, means on at least one of said cards and said mounting structure forming a complete circuit path when said last-mentioned card is engaged with terminals in tHe structure, safety circuit means switchable between set and reset states, said safety circuit means being switched to the set state in response to the interruption of said circuit path by removal of said one card forming said path from the mounting structure, means electrically connecting said safety circuit means with said control circuit means for preventing said control circuit means from supplying said operating signal when said safety circuit means is in the set state, and reset circuit means electrically connected to said safety circuit means for switching said safety circuit means from the set state to the reset state, said safety circuit means being resettable only when said circuit path is complete.
 2. The combination of claim 1 wherein said control circuit card comprises DC logic means adapted to receive said signals supplied by said transducer means for providing a DC control signal and means responsive to said DC control signal for supplying said operating signal and wherein said means electrically connecting said safety circuit means with said control circuit means for preventing said control circuit means from supplying said operating signal comprises means for preventing said DC control signal from being supplied to said means for supplying said operating signal when said safety circuit means is in the set state.
 3. The combination of claim 2 wherein said means for preventing said DC control signal from being supplied to said means for supplying said operating signal comprises an and-gate.
 4. The combination of claim 3 wherein said and-gate comprises two input terminals, one of said input terminals being electrically connected to the output terminal of said DC logic means, the other of said input terminals being electrically connected to said safety circuit means.
 5. The combination of claim 4 wherein said means responsive to said DC control signal for supplying said operating signal comprises DC-AC converter means for supplying an AC operating signal to operate said machine element.
 6. The combination of claim 1 wherein said reset circuit means comprises manually movable switch means electrically connected to said safety circuit means for switching the latter to the reset state.
 7. The combination of claim 6 including means for supplying an audible warning signal in response to operation of said switch means.
 8. The combination of claim 7 including means for delaying the resetting of said safety circuit means in response to operation of said switch means whereby said warning signal is provided before said safety circuit means is reset.
 9. In an electronic control for a machine, said control being of the type comprising a plurality of plug-in type circuit cards mechanically engageable with a plurality of terminals in a card-mounting structure, one of said cards being a control circuit card having DC logic means adapted to receive input signals in response to operation of selected elements of said machine and to provide a DC control signal, control circuit means responsive to said DC control signal for supplying an operating signal adapted to operate a particular element of said machine in response to said input signals, that improvement which comprises means on at least one of said cards and said mounting structure forming a complete circuit path when said one card is engaged with terminals in the structure, safety circuit means switchable between set and reset states, said circuit means being switched to the set state in response to the interruption of said circuit path by removal of said one card forming said path from the mounting structure, a reset circuit means electrically connected to said safety circuit means for switching said safety circuit means from the set state to the reset state, said safety circuit means being resettable only when said circuit path is complete, means electrically connecting said safety circuit means with said control circuit means for preventing said control circuit means from sUpplying said operating signal by preventing said DC control signal from being supplied to said means for supplying said operating signal when said safety circuit means is in the set state.
 10. In an electronic control for a machine, said control being of the type comprising a plurality of plug-in type circuit cards mechanically engageable with a plurality of terminals in a card-mounting structure, one of said cards being a control circuit card having DC logic means adapted to receive input signals in response to operation of selected elements of said machine and to provide a DC control signal, control circuit means responsive to said DC control signal for supplying an operating signal adapted to operate a particular element of said machine in response to said input signals, that improvement which comprises means on at least one of said cards and said mounting structure forming a complete circuit path when said one card is engaged with terminals in the structure, a flip-flop logic element switchable between set and reset states, said flip-flop being switched to the set state in response to the interruption of said circuit path by removal of said one card forming said path from the mounting structure, a reset circuit means electrically connected to said flip-flop logic element for switching said flip-flop logic element from the set state to the reset state, an and-gate electrically connecting said flip-flop logic element from the set state to the reset state, an and-gate electrically connecting said flip-flop logic element with said control circuit means for preventing said control circuit means from supplying said operating signal by preventing said DC control signal from being supplied to said control circuit means when said flip-flop logic element is in the set state, said and-gate comprising two input terminals, one of said input terminals being electrically connected to the output terminal of said DC logic means, the other of said input terminals being electrically connected to said flip-flop output terminal, said flip-flop logic element further comprising a pair of input terminals one of said flip-flop input terminals being electrically connected to said reset circuit means, the other of said flip-flop input terminals being electrically connected to said circuit path, said flip-flop logic element being switchable between set and reset states respectively in response to the respective application of signals at said last-mentioned flip-flop input terminal and said first-mentioned flip-flop terminal respectively, said flip-flop logic element being switchable to the reset state to provide a signal at said flip-flop output terminal only when said circuit path is complete, whereby said and-gate permits said DC control signal to be supplied to said control circuit means for supplying said operating signal.
 11. In combination an electronic control of the type comprising a plurality of plug-in type circuit cards mechanically engageable with a plurality of terminals in a card-mounting structure, a machine having an operable machine element, transducer means responsive to the operation of said machine, one of said circuit cards being a control circuit card having input terminals electrically connected to said transducer means for supplying an operating signal to operate said machine element including DC logic means adapted to receive said signals supplied by said transducer means for providing a DC control signal in response to signals supplied by said transducer means, means responsive to said DC control signal for supplying said operating signal, means on at least one of said cards and said mounting structure forming a complete circuit path when said last-mentioned card is engaged with terminals in the structure, a flip-flop logic element being switched to the set state in response to the interruption of said circuit path by removal of said one card forming said path from the mounting structure, reset circuit means electrically connected to said flip-flop logic element for Switching said flip-flop logic element from the set state to the reset state, an and-gate electrically connecting said flip-flop with said means responsive to said DC signal for preventing said last-mentioned means from supplying said operating signal when said flip-flop logic element is in the set state, said and-gate comprising two input terminals, one of said input terminals being electrically connected to the output terminal of said DC logic means, the other of said input terminals being electrically connected to said flip-flop output terminal, said flip-flop further comprising a pair of input terminals one of said flip-flop input terminals being electrically connected to said reset circuit means, the other of said flip-flop input terminals being electrically connected to said circuit path, said flip-flop logic element being switchable between set and reset states respectively in response to the respective application of signals at said last-mentioned flip-flop input terminal and said first-mentioned flip-flop terminal respectively, said flip-flop logic element being switchable to the reset state to provide a signal at said flip-flop output terminal only when said circuit path is complete.
 12. The control of claim 9 wherein said means for preventing said DC control signal from being supplied to said means for supplying said operating signal comprises an and-gate.
 13. The control of claim 12 wherein said and-gate comprises two input terminals, one of said input terminals being electrically connected to the output terminal of said DC logic means, the other of said input terminals being electrically connected to said safety circuit means. 